While washing the car earlier, I saw the caliper mount bolt slipping out from the front brake. Anyone knows how to install it back? I've been searching on the internet but was not able to find anything. When I looked up the part, it doesn't come with a nut, so not sure how to put it back.

 

Pretty sure that's a brake pad alignment pin and not a mounting bolt. Also pretty sure those are friction fit and do not have any type of fastener

 

Is it normal for it to slide out? I checked the other brake and I'm unable to pull it out. I just had my front brake pads and caliper replaced. But the technician said they did not have to touch that part to replace the pads and caliper.

 

Mine did the same thing after the dealer had to fix an issue with the front brakes. I returned the next day and it took them 20 minutes to fix it. Didn’t know what it was but I don’t like the idea of anything closely resembling a bolt looking loose. Even though it’s likely not required for them to function, look at the damage it could cause to the wheels!

 

The front 2015+ C63 S red calipers have one central "thru the caliper bolt + end-of-bolt screwbolt" that seems to be to set/hold/strengthen the spacing between caliper sides, 2 friction-fit pins that hold the retaining spring for the calipers (those 3 need to be removed when replacing brake pads) and bolts that hold the fixed calipers onto the steering/suspension parts (which need to be replaced to remove the caliper, replace a rotor, etc.). The bolts that attach the calipers are 1-time use bolts (i.e., are not to be re-used and must be replaced with new bolts after one tightening ... and the tightening is specific and critical, for safety).

If I found any such brake-assembly errors, I'd be _very_ concerned and have a talk with the service manager and/or shop foreman. Based upon their handling of that discussion, I'd decide whether to ever use that facility again. Brake and wheel/tire work should never be treated lightly and such work should always be double-checked prior to putting the vehicle back into service. Errors can be costly and dangerous.

 

User33 is correct. I will add, I would not drive the car to the location that performed the repairs - I would request that they trailer it. If that bolt slides out enough to contact the turning wheel while your driving, it will destroy your caliper beyond repair and may also do the same to your wheel. When I did my brakes, I lok-tight’ed the bolts in to prevent loosening.

 

I'm going to chime in again with my limited knowledge. Those absolutely are removed when replacing brake pads so whoever told you they are not is not qualified for the job. There is no bolt or nuts on what you show in the picture. That is a friction fit pin. If you sent that photo to someone and they indicated they did not touch that during the work they performed, they are incompetent or lying.

 

+1 to this. I just did my pads recently and pulling that pin is the only way to get your pads out.

 

Thank you everyone for the input. I brought the car back to the place (not dealer) that did the brake job. He is insisting that they did not remove the pads, which I know now is not true. He "fixed" the issue for me. I'l be taking the car to the dealer to have them check and make sure everything is good.